1. Field of the Invention
The present invention relates to a disk drive unit, such as an optical disk drive unit or a photomagnetic disk drive unit, for recording or reproducing information relative to a disk-shaped recording medium.
2. Description of the Prior Art
An example of a conventional disk drive unit, such as a photomagnetic disk drive unit, is described in Japanese First (unexamined) Patent Publication No. 6-195961. In this photomagnetic disk drive unit, a casing of the drive unit body is formed with an opening through which a radiator portion of an external magnetic field device is exposed to the exterior for effective heat radiation of an external magnetic field device. Further, a gap between the opening and the external magnetic field device is sealed by a closing member which expands or contracts depending on movement of the external magnetic field device.
Another example of an optical disk drive unit is described in Japanese First (unexamined) Patent Publication No. 6-295576. In this optical disk drive unit, an elastic sealing member is disposed between a base and a base cover so as to provide a closed structure of a casing which is formed by the base and the base cover. Further, a flexible printed circuit (FPC) board is used as a cable for connection to the exterior. The FPC is held between the base and the sealing member, with both end portions of the FPC board having an acute angle in section, so as to ensure a complete seal between the FPC board and the sealing member.
However, since each of the foregoing disk drive units aims to provide a closed structure for the whole casing, dust entering the casing upon insertion or ejection of a disk-shaped recording medium is diffused all over the inside of the casing so as to adhere to various internal components. Accordingly, dust accumulates on the optical head and circuit board over time. Mounted on the circuit board are components which may be subject to premature failure due to this accumulated dust, such as a primary amplifier for amplifying/modulating input/output signals relative to an optical head.
Further, to seal the entire casing, a large number of sealing members are required for sealing between the components which comprise the casing. This complicates the sealing structure maling the assembly of the casing relatively difficult.